This invention relates to systems for reactive gas phase processing such as chemical vapor deposition.
Chemical vapor deposition (“CVD”) reactors permit the treatment of substrates such as wafers mounted on a wafer carrier inside a reaction chamber. A component referred to as a gas distribution injector or injector head is mounted facing towards the wafer carrier. The injector typically includes a plurality of gas inlets that provide some combination of gases to the chamber for chemical vapor deposition. Some gas distribution injectors provide a shroud or carrier gases that assist in providing a laminar gas flow during the chemical vapor deposition process, where the carrier gas typically does not participate in chemical vapor deposition. Many gas distribution injectors have showerhead designs including gas inlets spaced in a pattern on the head.
A gas distribution injector typically permits the direction of precursor gases from gas inlets on an injector surface towards certain targeted regions of the reaction chamber where wafers can be treated for processes such as epitaxial growth of material layers. Ideally, the precursor gases are directed at the wafer carrier in such a way that the precursor gases react as close to the wafers as possible, thus maximizing reaction processes and epitaxial growth at the wafer surface.
In many metal organic chemical vapor deposition (MOCVD) processes, for example, combinations of precursor gases comprised of metal organics and hydrides, such as ammonia or arsine, are introduced into a reaction chamber through the injector. Process-facilitating carrier gases, such as hydrogen, nitrogen, or inert gases, such as argon or helium, also may be introduced into the reactor through the injector. The precursor gases mix in the reaction chamber and react to form a deposit on a wafer held within the chamber. The carrier gases typically aid in maintaining laminar flow at the wafer carrier.
In this way, epitaxial growth of semiconductor compounds such as, GaAs, GaN, GaAlAs, InGaAsSb, InP, ZnSe, ZnTe, HgCdTe, InAsSbP, InGaN, AlGaN, SiGe, SiC, ZnO and InGaAlP, and the like, can be achieved. Other gas treatment processes are performed for purposes other than epitaxial growth such as, for example, etching.
However, many existing gas injector systems have problems that may interfere with efficient operation or uniform deposition. For example, precursor injection patterns in existing gas distribution injector systems may contain significant “dead space” (space without active flow from gas inlets on the injector surface) resulting in recirculation patterns near the injector.
These recirculation patterns may result in prereaction of the precursor chemicals, causing unwanted deposition of reaction products on the injector. Additionally, unwanted deposition may occur on the wall of the reaction chamber. Such unwanted deposition consumes reactants and decreases the efficiency and reproducibility of the process. Moreover, reaction products deposited on the injector or on the reactor wall can be dislodged and can contaminate the substrates being processed. Thus, many current systems require frequent cleaning of the reactor, which further reduces productivity.
Considerable effort has been devoted in the art to achieving uniform reaction conditions over the entire extent of the wafer carrier, to assure that the deposited layers grow uniformly on all of the substrates. Another desire is to assure that the process gases supplied to all regions of the reactor are used efficiently and are not wasted. However, still further improvements in these aspects of operation would be desirable.
Thus, despite all of the efforts in this area, further improvement would be desirable.